Recently a notebook personal computer, a portable telephone, and the like in which a semiconductor integrated circuit is used have a sophisticated function more and more. As a result, there is an increased need for higher density and higher functionality of the semiconductor integrated circuit.
One of the method for realizing the high density and high functionality of the semiconductor integrated circuit is to laminate the wafer. In order to laminate the wafer, it is necessary that, after bonding electrodes are formed in wafer surfaces in which the circuit is already formed, the electrodes of two wafers or an already laminated wafer and wafer to be laminated next be brought into contact with and bonded to each other. In cases where wafer electrodes are bonded to each other, it is important to evenly bring the electrodes into contact with each other and to activate the electrode bonding surfaces. In order to evenly bring the electrodes into contact with each other, it is necessary to improve flatness of the bonding interface. The wafers are, for example, heated to activate the electrode bonding surfaces.
Therefore, there is developed an apparatus, which bonds the wafers while pressurizing and heating the wafers (for example, see Japanese Patent Application Laid-Open No. 2005-302858).
FIG. 15 is a view showing cross sections of two wafers 201U and 201L to be bonded. Irregularities of 3 to 5 micrometers exist in the surface of the wafer (FIG. 15A). The irregularities are caused by a variation in wafer thickness. Pressures are applied to the two laminated wafers 201U and 201L from both sides to improve the flatness of the wafer bonding interface. In this case, when the wafer bonding interface becomes flat, a variation in wafer thickness emerges in an opposite surface to the wafer bonding interface (FIG. 15B). Accordingly, in order to eliminate an influence of the variation in wafer thickness on the flatness of the wafer bonding interface, it is necessary that the variation in wafer thickness be absorbed while pressurizing and heating are performed.
In order to improve the flatness of the wafer bonding interface, it is necessary to change a shape of a pressurizing surface.
However, conventionally there has not been developed a wafer bonding apparatus in which a shape of a pressurizing surface is changed to absorb the variation in wafer thickness while the pressurizing and heating are performed in order to improve the flatness of the wafer bonding interface.